In the first part of the pooled analysis, the researchers examined the QT interval - a segment of the heart's rhythm - of 93 people who had just consumed one to three cans of energy drinks.

They found that the QT interval was 10 milliseconds longer for those who had consumed the energy drinks.

The QT interval describes a segment of the heart's rhythm on an electrocardiogram; when prolonged, it can cause serious irregular heartbeats or sudden cardiac death.

Lead author Doctor Sachin Shah, assistant professor at University of the Pacific in the United States, said: 'Doctors are generally concerned if patients experience an additional 30 milliseconds in their QT interval from baseline.

'QT prolongation is associated with life-threatening arrhythmias. The finding that energy drinks could prolong the QT, in light of the reports of sudden cardiac death, warrants further investigation.'

The researchers also found that the systolic blood pressure, the top number in a blood pressure reading, increased an average of 3.5 points in a pool of 132 participants.

Doctors have warned the drinks may disturb the heart's natural rhythm

Dr Shah added: 'The correlation between energy drinks and increased systolic blood pressure is convincing and concerning, and more studies are needed to assess the impact on the heart rhythm.

'Patients with high blood pressures or long QT syndrome should use caution and judgment before consuming an energy drink.

'Since energy drinks also contain caffeine, people who do not normally drink much caffeine might have an exaggerated increase in blood pressure.

'People with health concerns or those who are older might have more heart-related side effects from energy drinks.'

The findings were presented at the American Heart Association's Epidemiology and Prevention conference.